GB1579370A

GB1579370A - Centrifuge

Info

Publication number: GB1579370A
Application number: GB13773/77A
Authority: GB
Original assignee: Hein G H
Current assignee: Hein G H
Priority date: 1976-04-29
Filing date: 1977-04-01
Publication date: 1980-11-19
Also published as: CH610531A5; JPS52145680U; CA1063990A; US4046317A; JPS5710777Y2; SE7704865L; DE2719261A1

Description

PATENT SPECIFICATION

( 11) 1 579 370 ( 21) Application No 13773/77 ( 22) Filed 1 April 1977 ( 31) Convention Application No.

681 313 ( 32) Filed 29 April 1976 in ( 33) United States of America (US) ( 44) Complete Specification published 19 Nov 1980 ( 51) INT CL 3 B 04 B 9/12 9/06 ( 52) Index at acceptance B 2 P 9 A 3 A 9 B 9 D 1 9 D 3 9 G F 2 A 302 D 36 ( 72) Inventor GEORGE NORTON HEIN JR ( 54) CENTRIFUGE ( 71) I, GEORGE NORTON HEIN, JR, a Citizen of the United States of America residing at 331 Chesham Avenue, San Carlos, California 94070, United States of America, do hereby declare the invention, for which I pray that a patent may be granted to me, and the method by which it is to be performed, to be particularly described in and by the following statement:This invention relates to a centrifuge incorporating an improved apparatus for holding and stabilising the centrifuge rotor during its deceleration.

In order to separate certain fluid mixtures, very high speeds of rotation are required For example, separation of protein, viruses and other various clinical specimens require extremely high speeds of centrifugation in order to separate fractions thereof within reasonable time spans It has been found that extremely high rotational speeds such as 150,000 r p m to 200,000 r.p m can be obtained by rotating a centrifuge rotor on a cushion of air with pressurised air streams An example of such an air driven centrifuge is illustrated in U S.

Patent Specification No 3,456,875.

In the case of air driven centrifuges, when the driving air has been shut down after the centrifugation of the fluid mixture, a secondary supporting supply of air must be introduced between the rotor and rotor seat to hold the rotor off the rotor seat as the rotor decelerates to a stop However, in some present devices because of the location of the flutes on the rotor the introduction of a supporting air supply will never allow the rotor completely to stop, since this air movement across the rotor flutes will tend to continue driving the rotor slightly on the supporting air This supporting air is generally introduced along the outer frustoconical portion of the rotor seat adjacent the location of the driving air jets.

In some instances, the orientation of the driving air jets is reversed not only to supply supporting air, but also to aid in the deceleration of the rotor to a stop In some cases the use of the reversing air jets may cause 50 the start of a reverse rotation of the rotor after it has stopped Consequently, many arrangements now used do not provide a friction free cushion of air which allows the rotor to decelerate independent of any driv 55 ing effects of the supporting air.

A significant problem also exists with respect to the inherent design of every rotor in addition to the characteristics of the test mixtures in the rotor, presenting certain 60 parameters which create critical speeds where the rotor will precess, wobble or vibrate excessively while decelerating These critical speeds are usually relatively low rotational speeds and the precession and/or 65 wobbling can become so great as to cause the sample to be remixed or to cause the rotor to contact the sidewalls of the seat, causing the rotor to become misaligned from its rotational axis and thrash around 70 within the centrifuge housing.

Consequently, some prior art arrangements incorporate a stabilising means physically to contact or guide the rotor as it experiences these slow critical speeds to 75 help eliminate the above-described undesirable effects The supporting air in these devices provide sufficient stabilisation to overcome the problems encountered during the critical speeds of the rotor, but such 80 stabilising devices must be quite delicate in design to provide the requisite stabilising and are subject to constant wear.

In addition, other supporting air arrangements used heretofore tend to 85 establish a cushion of air which causes the rotor to ride somewhat high within the rotor seat In other words, the rotor is separated.

from the surface of the rotor seat more than desirable, rendering the rotor more suscept 90 t_ om 1 579 370 ible to various unstabilising conditions and possible ejection from the rotor seat.

In accordance with the present invention there is provided a centrifuge comprising a rotor; a rotor seat for receipt of the lower portion of the rotor; driving means for rotating said rotor; the rotor being formed with a central recessed portion, and the rotor seat being formed with a central projecting portion, said recessed and projecting portions being of complementary shapes and dimensions to establish therebetween a specific confined flow path between the rotor and the rotor seat; and means located in the central portion of the rotor seat for introducing a supply of supporting air into said flow path, when said driving means is not operating at such a velocity that the air pressure in said flow path is below atmospheric pressure to hold the rotor within the rotor seat and allow the rotor to decelerate to a stable stop.

An embodiment of the present invention will now be described by way of example with reference to the accompanying drawings, in which:

Fig 1 is a sectional elevation view of an air driven centrifuge according to the present invention; Fig 2 is an enlarged view of a detail in Fig 1; Fig 3 is a perspective view of the rotor showing the lower end of the conical recess in the rotor; and Fig 4 is a perspective view of the rotor seat showing the central conical projection and the outer frustoconical portion.

An air driven centrifuge 10 is shown in Fig 1 A removable cover 12 is situated over a rotor housing 14 The overall housing 14 is enclosed by an outer casing 16 The housing 14 in conjunction with the cover 12 forms a rotor chamber 18 in which is situated a rotor seat 20 adjacent the bottom 22 of the chamber 18 for receipt of a rotor 24.

It should be noted that the cover 12 contains a braking apparatus 26 in the present embodiment wherein a non-magnetic carrier 28 shifts a magnet or series of magnets toward and away from the rotor 24 for quickly decelerating the rotation of the rotor 24 in the housing 14 The spring 32 forces the carrier 28 toward the rotor 24 for quick braking of the rotor while the introduction of air pressure through air passage 34 will move the carrier 28 away from the rotor, allowing free rotation of the rotor.

The operation and structure of the braking apparatus 26 is shown in more detail in a copending application No 13769/77 (Serial No 1572427) filed on even date herewith entitled An Eddy Current Brake for an Air Driven Centrifuge.

The rotor seat 20, shown in more detail in Fig 2, is comprised of a generally cylindrical stator body 36 having a depending central portion 38 and an annular flange portion 40.

Located within the annular flange portion of the stator body 36 is a stator cavity 42 which contains the stator pad 44 The bottom of the stator pad 44 has a plurality of 70 extended portions or feet 46 which rest on the bottom 48 of the stator cavity 42 The diameter of the inner surface 50 and the diameter of the outer surface 52 of the stator pad are respectively greater and smal 75 ler than the diameter of the inner surface 54 and the outer surface 56 of the stator cavity 42 Therefore, the stator pad 44 is permitted to move in a precessional manner to accommodate slight movement of the rotor 80 24 in a direction lateral to its rotational axis.

The stator pad 44 provides stability to the rotation of the rotor 24 within the rotor seat 20.

Located adjacent the depending central 85 portion 38 of the stator body 36 is an annular manifold 60 which is in fluid communication with a driving air passage 58 The stator body 36 contains a series of driving air jets 64 which are in fluid communication with 90 the annular manifold 60 The annular flange portion 40 of the stator body is sealed against the housing 14 by a sealing 0-ring 66 while the depending central portion 38 of the stator body is sealed against the housing 95 by a second sealing 0-ring 68.

Extending through the center of the depending central portion 38 of the stator body is an air levitation flow conduit 62 which is aligned and in fluid communication 100 with a supporting or holding air jet 74 centrally located in the rotor seat 20.

The rotor 24, which is, in a preferred embodiment, approximately one and onehalf inches in diameter, is situated within the 105 rotor chamber 18 with its lower portion 80 positioned within the rotor seat 20 As shown more clearly in Figure 3, the lower portion 80 of the rotor 24 has a frustoconical area 82 which is sloped inward and has 110 on its surface a series of flutes 84 that receive the pressurized air from the air jets 64 of Figure 2 to rotate the rotor 24 at high rotational speeds to subject the sample mixtures within the rotor to the centrifugal 115 forces for segregating out various constituents With respect to Figure 3, the central area 86 within the lower portion 80 of the rotor has a recessed conical shape extending inward from the smallest cir 120 cumferential edge 81 of the frustoconical area 82 As shown in Figure 4, the central area 88 of the rotor seat 20 has a slight conical shape projecting outward which has a base circumferential edge 89 Located at the 125 apex 90 of the central area 88 in the rotor seat is the air levitation jet 74 The outer area 92 of the rotor seat is in the shape of an inverted frustocone Part of the outer area 92 of the rotor seat 20 is comprised of the 130 1 579 370 sloping surface 94 on the stator pad 44.

Therefore, the supporting area of the rotor seat 20 which receives the lower portion 80 of the rotor is comprised of the central cone area 88, the portion 96 of the inverted frustoconical surface on the stator body 36, and the sloping surface 94 of the stator pad 44.

As shown in Figure 2, the central area 86 in the lower portion 80 of the rotor mates or nests somewhat with the central area 88 of the rotor seat while the frustoconical portion 82 of the lower portion 80 of the rotor mates or nests with the frustoconical portions 94 and 96 of the rotor seat 20 The respective recessed central conical area 86 in the rotor in conjunction with the projecting conical central area 88 of the rotor seat forms a conical flow path 98 for the air exiting the air jet 74 Further, the frustoconical shape of the outer area 82 of the rotor lower portion 80 in conjunction with the frustoconical shape of the outer portions 94 and 96 of the rotor seat provides a frustoconical flow path 100 in fluid communication with the conical flow path 98 through which the air proceeds from the air jet 74 out into the rotor chamber 18.

Turning to the operation of the present invention, attention is directed to Figure 1 where the rotor 24, containing a fluid mixture for centrifugation to separate out various constituents in the fluid mixture, is placed within the rotor chamber 18 The lower portion 80 of the rotor is positioned within the supporting area of the rotor seat It should be noted, however, that the sloping surface 94 of the stator pad 44 has a slightly steeper slope than that of the frustoconical portion 96 in the stator body 36.

Therefore, the rotor 24, when at rest and nesting within the rotor seat 20, bears primarily on the stator pad 44, but also may contact or come closely adjacent to the conical central area 88 of the rotor seat.

An air supply conduit 102 provides air under pressure by control of the valve 103 through supply line 104 and through coupling 106 to supply line 58 The air proceeding through line 104 flows into passage 34 in the cover 12 to force the braking apparatus away from the rotor to allow free rotation of the rotor as explained in more detail in the previously referenced application for an Eddy Current Brake The air proceeding through line 58 enters the annular manifold where it proceeds through a plurality of air jets 64 that impinge air under pressure on the rotor flutes 84, causing the rotor 24 to rotate at very high speeds The air that is introduced from the air driving jets 64 and onto the flutes 84 process out between the rotor and the stator pad 44 into the rotor chamber 18 where it exists the centrifuge through the exit ports 17 and 19 Further, the driving air also holds the rotor 24 on a cushion of air above the rotor seat 20 for support upon which the high speed rotation occurs.

It should be noted that alternate driving means, such as an electromagnetic driving 70 mechanism, could be utilized to drive the rotor in conjunction with the air levitation arrangement of the present invention.

When the centrifugation operation has been completed, the valve 103 is moved to 75 stop the flow of air through the supply lines 104 and 58 At the same time the valve 103 permits a supply of pressurized air from the air supply conduit 102 to flow through a coupling 72 and into an air levitation supply 80 line 62 for flow into the air levitation jet 74.

The capacity of the air conduit 62 from the air supply conduit 102 to the air levitation jet 74 should preferably be sufficiently larger than the capacity of the air conduit 58 85 from the air supply conduit 102 to the air driving jets 64, so that there is a slight dwell between the cessation of the air flow exiting the air driving jets 64 and the commencement of the air flow exiting the air levitation 90 jet 74 It is preferable that the air flow is not exiting both the air levitation jet 74 and the air driving jets 64 at the same time, because some instability may be introduced to the rotor 24 Consequently, the longer or grea 95 ter capacity of the air passage 62 between the air supply conduit 102 and the air levitation jet 74 provides the desirable delay in the air flow exiting the levitation jet until the air flow exiting the air drive jets 64 has 100 ceased Although the preferable mode of operation is to not have the driving air and the levitation air contacting the rotor at the same time, an arrangement of having both the driving and levitation air contacting the 105 rotor simultaneously at various stages of the operation would be permissible without adversely affecting the stability of the rotor.

The air under pressure exiting the levitation jet 74 proceeds along the conical flow 110 path 98 and into the frustoconical flow path from which is exits into the rotor chamber 18 Since the air is flowing in a smooth path generally parallel with the frustoconical flow path 100, essentially no forc 115 ing air impinges upon the rotor flutes 84, allowing the rotor 24 to coast freely during deceleration and braking by the braking apparatus 26.

Because the air flowing from the air levi 120 tation jet 74 and through the conical flow path 98 and the frustoconical flow path 100 is proceeding at a significant velocity, the air pressure in the space between the rotor 24 and the rotor seat 20 is reduced to blow 125 atmospheric pressure due to the Bernouilli's principle that, as air increases speed, air pressure will decrease Therefore, the atmospheric pressure surrounding the majority of the rotor 24 will hold the rotor 130 1 579 370 stable and secure in the rotor seat 20 Consequently, the rotor 24 will ride down within the rotor seat where the separation of the rotor and rotor seat may be as little as approximately five thousandths of an inch.

The ability to hold the rotor closely within the rotor seat is particularly important during the deceleration phases of the rotor when it reaches critical speeds that might tend to induce vibration and wobbling.

In addition, the slight conical central portion 88 of the rotor seat 20 and the slight conical central recessed area 86 in the rotor provide an aid in conjunction with the stator pad 44 in maintaining the rotational stability of the rotor, keeping its rotational axis aligned with the central axis of the rotor seat Although the slight conical surfaces in the central portion 88 of the rotor seat and the central area 86 of the rotor have been constructed with approximately a five degree optimum slope, it is envisoned that the slope can be in the preferred range of three to ten degrees and still permit the proper air levitation of the rotor for a stable deceleration of the rotor Furthermore, a slope as high as forty-five degrees has been successfully used, but the lateral clearance between the respective surfaces 86 and 88 in Figure 2 becomes quite small as compared to the lateral clearance between the surfaces 86 and 88 with a lesser degree slope Consequently, the steepness of the slope reduces the lateral movement tolerance of the central area 86 of the rotor 24 on central portion 88 of the rotor seat 20 The spacing between the central area 86 of the rotor and the cental portion 88 of the rotor seat to accommodate lateral movement of the rotor decreases as the steepness of the conical slope increases As this spacing decreases in size it becomes a significant factor during critical speeds of the rotor when it may tend to wobble and incur some lateral movement, resulting in an undesired contact between the central area 86 of the rotor with the central portion 88 of the rotor seat while the rotor is still spinning.

The rotor 24 and stator pad 44 can move laterally if necessary for compensation of critical speeds, but they will not move to an extent where the conical surfaces could contact or separate to such an extent that the generation of the Bernouilli forces would be hampered.

It should be noted that the projecting conical area 88 of the rotor seat could be in the configuration of a partial speherical surface rather than a cone while the recessed central portion 86 of the lower end 80 of the rotor could be in the configuration of a mating partial spherical surface.

Claims

WHAT I CLAIM IS:-

1 A centrifuge comprising a rotor; a rotor seat for receipt of the lower portion of the rotor; driving means for rotating said rotor; the rotor being formed with a central recessed portion, and the rotor seat being formed with a central projecting portion, said recessed and projecting portions being 70 of complementary shapes and dimensions to establish therebetween a specific confined flow path between the rotor and the rotor seat; and means located in the central portion of the rotor seat for introducing a sup 75 ply of supporting air into said flow path, when said driving means is not operating, at such a velocity that the air pressure in said flow path is below atmospheric pressure to hold the rotor within the rotor seat and 80 allows the rotor to decelerate to a stable t A centrifuge as claimed in Claim 1, wherein said introducing means comprises supporting air jet means located in the 85 center of said rotor seat.

3 A centrifuge as claimed in either preceding claim, wherein said driving means comprises air jets connected to a first air passage from an air supply source and said 90 introducing means is connected to a second air passage from said air supply source, said second air passage having an air capacity greater than the air capacity of said first air passage 95 4 A centrifuge as claimed in any preceding Claim, wherein said central recessed portion has a conical shape, and said projecting central portion has a conical shape.

A centrifuge as claimed in any one of 100 Claims 1-3, wherein the central recessed portion has a partial spherical shape, and said projecting central portion has a partial spherical shape.

6 A centrifuge as claimed in any pre 105 ceding Claim, wherein said projecting central portion in the rotor seat and forms in conjunction with said recessed portion in the bottom of said rotor a conical air flow path in a generally downward direction and 110 the outer portion of said rotor seat forms in conjunction with a sloping outer area in the lower portion of said rotor a frustoconical air flow path in a generally upward direction, said conical flow path being in fluid 115 communication with said frustoconical flow path, so that air from said introducing means can flow sequentially through said conical flow path and into said frustoconical flow path to hold the rotor securely centered 120 over said rotor seat on a cusion of air when said driving air jet means is not operating.

7 A centrifuge substantially as hereinbefore described with reference to the accompanying drawings 125 FITZPATRICKS, (Chartered Patent Agents), 14-18 Cadogan Street, Glasgow G 2 6 QW.

-and1 579370 5 Warwick House, Warwick Court, London WC 1 R 5 DJ.

Printed for Her Majesty's Stationery Office by The Tweeddale Press Ltd, Berwick-upon-Tweed, 1980 Published at the Patent Office, 25 Southampton Buildings, London, WC 2 A l AY, from which copies may be obtained.